The present invention relates to a process for preparing block copolymers, block copolymers prepared by the process, additive concentrates and lubricating oil compositions.
The viscosity of oils of lubricating viscosity is generally dependent upon temperature. As the temperature of the oil is increased, the viscosity usually decreases, and as the temperature is reduced, the viscosity usually increases.
The function of a viscosity improver is to reduce the extent of the decrease in viscosity as the temperature is raised or to reduce the extent of the increase in viscosity as the temperature is lowered, or both. Thus, a viscosity improver ameliorates the change of viscosity of an oil containing it with changes in temperature. The fluidity characteristics of the oil are improved.
Viscosity improvers are usually polymeric materials and are often referred to as viscosity modifiers or viscosity index improvers. Block copolymers are a known class of viscosity improvers.
Dispersants are also well-known in the lubricating art. Dispersants are employed in lubricants to keep impurities, particularly those formed during operation of mechanical devices such as internal combustion engines, automatic transmissions, etc. in suspension rather than allowing them to deposit as sludge or other deposits on the surfaces of lubricated parts.
Multifunctional additives that provide both viscosity improving properties and dispersant properties are likewise known in the art. Such products are described in numerous publications including Dieter Klamann, xe2x80x9cLubricants and Related Productsxe2x80x9d, Verlag Chemie Gmbh (1984), pp 185-193; C. V. Smalheer and R. K. Smith xe2x80x9cLubricant Additivesxe2x80x9d, Lezius-Hiles Co. (1967); M. W. Ranney, xe2x80x9cLubricant Additivesxe2x80x9d, Noyes Data Corp. (1973), pp 92-145, M. W. Ranney, xe2x80x9cLubricant Additives, Recent Developmentsxe2x80x9d, Noyes Data Corp. (1978), pp 139-164; and M. W. Ranney, xe2x80x9cSynthetic Oils and Additives for Lubricantsxe2x80x9d, Noyes Data Corp. (1980), pp 96-166. Each of these publications is hereby expressly incorporated herein by reference.
Dispersant-viscosity improvers are generally prepared by functionalizing, i.e., adding polar groups, to a hydrocarbon polymer backbone.
Hayashi, et al, U.S. Pat. No. 4,670,173 relates to compositions suitable for use as dispersant-viscosity improvers made by reacting an acylating reaction product which is formed by reacting a hydrogenated block copolymer and an alpha-beta olefinically unsaturated reagent in the presence of free-radical initiators, then reacting the acylating product with a primary amine and optionally with a polyamine and a mono-functional acid.
Chung et al, U.S. Pat. No. 5,035,821 relates to viscosity index improver-dispersants comprised of the reaction products of an ethylene copolymer grafted with ethylenically unsaturated carboxylic acid moieties, a polyamine having two or more primary amino groups or polyol and a high functionality long chain hydrocarbyl substituted dicarboxylic acid or anhydride.
Van Zon et al, U.S. Pat. No. 5,049,294, relates to dispersant/VI improvers produced by reacting an alpha, beta-unsaturated carboxylic acid with a selectively hydrogenated star-shaped polymer then reacting the product so formed with a long chain alkane-substituted carboxylic acid and with a C1 to C18 amine containing 1 to 8 nitrogen atoms and/or with an alkane polyol having at least two hydroxy groups or with the performed product thereof.
Bloch et al, U.S. Pat. No. 4,517,104, relates to oil soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties then with polyamines having two or more primary amine groups and a carboxylic acid component or the preformed reaction product thereof.
Gutierrez et al, U.S. Pat. No. 4,632,769, describes oil-soluble viscosity improving ethylene copolymers reacted or grafted with ethylenically unsaturated carboxylic acid moieties and reacted with polyamines having two or more primary amine groups and a C22 to C28 olefin carboxylic acid component.
Each of these patents is hereby expressly incorporated herein by reference.
For additional disclosures concerning multi-purpose additives and particularly viscosity improvers and dispersants, the disclosures of the following United States patents are incorporated herein by reference:
U.S. Pat. No. 5,530,079, Veregin et al., discloses a polymerization process comprising heating a mixture of a free radical initiator, a stable free radical agent, at least one polymerizable monomer compound, and optionally a solvent.
U.S. Pat. No. 5,401,804, Georges et al., discloses a free radical polymerization process comprising heating a mixture of a free radical initiator, a stable free radical agent, and at least one polymerizable monomer. The stable free radical agent includes nitroxide free radicals. An organic sulfonic or carboxylic acid can be added to increase the rate of polymerization.
U.S. Pat. No. 3,189,663, Nozaki, discloses block copolymers comprising copolymers where the macromolecules are made up of at least two different linear segments. The first is made up of a linear polymer of a member of the group consisting of ethylenically unsaturated carboxylic acids, anhydrides thereof, and their esters and amides. The second segment is made up of a polymer of a dissimilar member of the first group, esters of unsaturated alcohols and saturated acids, alkenes, alkadienes, vinyl halides, vinyl substituted aromatic hydrocarbons, alkenyl-substituted halo-hydrocarbons, and alkenyl ethers.
U.S. Pat. No. 4,581,429, Solomon et al., discloses a process for free radical polymerization to produce relatively short chain length homo- and copolymers. The initiator has the general formula 
U.S. Pat. No. 5,608,023, Odell et al., discloses a polymerization process comprising heating a mixture of a free radical initiator, a stable free radical agent, at least one polymerizable monomer compound, and a sulfonic acid salt polymerization rate enhancing compound to form thermoplastic resins.
U.S. Pat. No. 5,449,724, Moffatt et al., discloses a free radical polymerization process which includes heating a mixture comprised of a free radical initiator, a stable free radical agent, and ethylene.
U.S. Pat. No. 5,677,388, Koster et al., relates to a living free-radical polymerization process for preparing polymers from vinyl aromatic monomers comprising polymerizing the vinyl aromatic monomer in the presence of a difunctional nitroxyl initiator.
An object of this invention is to provide a novel process for preparing block copolymers.
Another object is to provide a one-pot, relatively short duration process for preparing block copolymers.
Another object is to provide block copolymers which may be isolated as diluent-free, dry, free-flowing solids.
Another object of this invention is to provide novel block copolymers useful as lubricant additives.
Still another object is to provide lubricants having improved shear stability and viscometric properties.
A more specific object is to provide additives directed to improving lubricant viscometrics.
Other objects will in part be obvious in view of this disclosure and will in part appear hereinafter.
The present invention provides a process for preparing a block copolymer. In one embodiment, the block copolymers comprise (A) a poly (vinyl aromatic) block and (B) a poly (vinyl aromatic-co-acrylic) block, said process comprising the steps,
(a) polymerizing at an elevated temperature from about 5 to about 95 mole % of a charge comprising at least one vinyl aromatic monomer to prepare a stabilized active polymer block (A), using a free radical polymerization process,
wherein a stable free radical agent is employed during the polymerization, thereby preserving the stabilized active polymerization site at the terminus of the poly (vinyl aromatic) block (A);
(b) adding at least one acrylic monomer and optionally, additional vinyl aromatic monomer, to the mixture of residual vinyl aromatic monomer and stabilized active polymer block of (a); and
(c) further reacting the mixture of (b) using a free radical process to effect copolymerization of said monomers, thereby preparing a poly(vinyl aromatic-co-acrylate) block (B).
The present invention also relates to block copolymers prepared by the above process, additive concentrates for preparing lubricating oil compositions and lubricating oil compositions. In other embodiments, the present invention relates to block copolymers having more than two blocks.
As used herein, the terms xe2x80x9chydrocarbonxe2x80x9d, xe2x80x9chydrocarbylxe2x80x9d or xe2x80x9chydrocarbon basedxe2x80x9d mean that the group being described has predominantly hydrocarbon character within the context of this invention. These include groups that are purely hydrocarbon in nature, that is, they contain only carbon and hydrogen. They may also include groups containing substituents or atoms which do not alter the predominantly hydrocarbon character of the group. Such substituents may include halo-, alkoxy-, nitro-, etc. These groups also may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for example, sulfur, nitrogen and oxygen. Therefore, while remaining predominantly hydrocarbon in character within the context of this invention, these groups may contain atoms other than carbon present in a chain or ring otherwise composed of carbon atoms provided that they do not adversely affect reactivity or utility of the process or products of this invention.
In general, no more than about three non-hydrocarbon substituents or hetero atoms, and preferably no more than one, will be present for every 10 carbon atoms in the hydrocarbon or hydrocarbon based groups. Most preferably, the groups are purely hydrocarbon in nature, that is, they are essentially free of atoms other than carbon and hydrogen.
Throughout the specification and claims the expression oil soluble or dispersible is used. By oil soluble or dispersible is meant that an amount needed to provide the desired level of activity or performance can be incorporated by being dissolved, dispersed or suspended in an oil of lubricating viscosity. Usually, this means that at least about 0.001% by weight of the material can be incorporated into a lubricating oil. For a further discussion of the terms oil soluble and dispersible, particularly xe2x80x9cstably dispersiblexe2x80x9d, see U.S. Pat. No. 4,320,019 which is expressly incorporated herein by reference for relevant teachings in this regard.
The expression xe2x80x9clowerxe2x80x9d is used throughout the specification and claims. As used herein to describe various groups, the expression xe2x80x9clowerxe2x80x9d is intended to mean groups containing no more than 7 carbon atoms, more often, no more than 4, frequently one or two carbon atoms.
It must be noted that as used in this specification and appended claims, the singular forms also include the plural unless the context clearly dictates otherwise. Thus the singular forms xe2x80x9caxe2x80x9d, xe2x80x9canxe2x80x9d, and xe2x80x9cthexe2x80x9d include the plural; for example xe2x80x9ca monomerxe2x80x9d includes mixtures of monomers of the same type. As another example the singular form xe2x80x9cmonomerxe2x80x9d is intended to include both singular and plural unless the context clearly indicates otherwise.
In the context of this invention the term xe2x80x9ccopolymerxe2x80x9d means a polymer derived from two or more different monomers. Thus, a polymer derived from a mixture of, for example, methyl-, butyl-, C9-11-, and C12-18- methacrylates, or a polymer having two or more distinct blocks, is a copolymer as defined herein. The copolymers of this invention also may contain units derived from nitrogen-containing monomers.
The expression xe2x80x9csubstantially inertxe2x80x9d is used in reference to diluents. When used in this context, xe2x80x9csubstantially inertxe2x80x9d means the diluent is essentially inert with respect to any reactants or compositions of this invention, that is, it will not, under ordinary circumstances, undergo any significant reaction with any reactant or composition, nor will it interfere with any reaction or composition of this invention.
The expression viscosity index (often abbreviated VI) is frequently used herein. Viscosity index is an empirical number indicating the degree of change in viscosity within a given temperature range. A high VI signifies an oil that displays a relatively small change in viscosity with temperature.
The Vinyl Aromatic Monomer
In the present invention one of the monomers is a vinyl substituted aromatic compound
The vinyl substituted aromatics generally contain from 8 to about 20 carbons, preferably from 8 to 12 carbon atoms and most preferably, 8 or 9 carbon atoms. Heterocyclic compounds having, for example sulfur, oxygen or nitrogen ring heteroatoms, such as vinyl pyridines are contemplated.
Examples of vinyl substituted aromatics include vinyl anthracenes, vinyl naphthalenes and vinyl benzenes (styrenes) including substituted styrenes. Substituted styrenes include styrenes that have substituents on the ring or on the vinyl group. Such substituents include halo-, amino-, alkoxy-, carboxy-, hydroxy-, sulfonyl-, hydrocarbyl- wherein the hydrocarbyl group has from 1 to about 12 carbon atoms, and other substituents. Examples of styrenes include styrene, alpha-lower alkyl substituted styrene, for example, alpha-methyl styrene and alpha-ethyl styrene, styrenes having ring substituents, preferably, lower alkyl ring substituents, for example, ortho-methyl styrene, meta-methyl styrene, para-methyl styrene, and para-tertiary-butylstyrene, vinyl benzene sulfonic acid, and para-lower alkoxy styrene. Mixtures of two or more vinyl aromatic monomers can be used. Styrene is preferred.
The Acrylic Monomer
As used herein the term xe2x80x9cacrylic monomerxe2x80x9d includes acrylic acids, esters of acrylic acids, acrylic amides, and acrylonitriles and the corresponding alkacryl-, especially methacryl-, compounds, particularly alkyl methacrylates, methacrylamides, and methacrylonitrile. The esters of acrylic acids typically contain from 2 to about 50 carbon atoms in the ester group, which ester group includes the carbonyl carbon atom. Often, the ester groups are lower alkyl esters, wherein the expression xe2x80x9clower alkylxe2x80x9d means alkyl groups having fewer than 7 carbon atoms, preferably from 1 to about 4 carbons. In another preferred embodiment, the ester group contains from 2 to about 30 carbon atoms, preferably from about 9 to about 23 carbon atoms, often from about 8 to about 18 carbon atoms. In an especially preferred embodiment, the ester group contains a mixture of alkyl groups, such as from about 9 to about 11 carbon atoms, from about 11 to about 16 carbon atoms or from about 13 to about 16 carbon atoms. As defined herein, the expression xe2x80x9cester groupxe2x80x9d includes the ester carbonyl carbon atom. Thus, for example, a methyl ester contains two carbon atoms in the ester group.
Examples of useful acrylic monomers include acrylic acid, methacrylic acid, esters thereof, including lower alkyl esters, fatty esters, and mixed esters, such as C8-10 alkyl esters and C12-15 alkyl esters, acrylamide, methacrylamide, and N- and N,N-substituted acrylamides and the corresponding methacrylamides, acrylonitrile and methacrylonitrile.
Also included among acrylic monomers are xcex1,xcex2-unsaturated polycarboxylic monomers or functional equivalents thereof. Encompassed within this group are acids, carbonyl halides, esters, acid-esters, anhydrides, amides, amidic acids and esters thereof. These include acids such as maleic acid, fumaric acid, crotonic acid, citraconic acid, itaconic acid and mesaconic acid, as well as their corresponding anhydrides, carbonyl halides, amides, amidic acids, amidic esters, and the full and partial esters (especially lower alkyl esters) thereof. Maleic acid and maleic anhydride, especially the latter, are particularly preferred, as are the corresponding fumaric and itaconic compounds.
In one embodiment, instead of employing monomers that are derivatives of acrylic acid or anhydride monomers, copolymers may be prepared employing an acid or anhydride monomer then reacting the acid or anhydride containing copolymer with a suitable alcohol and/or amine to generate a copolymer containing ester and/or amide groups. These are particularly valuable when the copolymer is intended for use as a performance enhancing additive for lubricants or fuels.
Preferably, the vinyl aromatic monomer is selected from the group consisting of styrenes and the acrylic monomer is selected from the group consisting of acrylic acids, esters of acrylic acids, acrylic amides, and acrylonitriles, maleic acid and maleic anhydride. More preferably, the styrenes comprise at least one of styrene, an xcex1-lower alkyl substituted styrene, vinyl benzene sulfonic acid, and styrenes having C14 alkyl ring substituents, especially styrene, and the acrylic monomer comprises at least one methacrylic acid ester. In another preferred embodiment, the acrylic monomer comprises maleic anhydride.
Stable Free Radical Agent
Stable free radical agents are known. Suitable stable free radical agents include phenoxy radicals and nitroxy radicals. Examples of phenoxy radicals include phenoxy radicals substituted in the 2 and 6 positions by bulky groups such as tert-alkyl (e.g., t-butyl), phenyl, or dimethylbenzyl, and optionally substituted at the 4 position by an alkyl, alkoxyl, aryl, or aryloxy group or by a heteroatom containing group (e.g., S, N, or O) such as a dimethylamino or diphenylamino group, and materials which contain two or more such aromatic rings bridged at, e.g., the 4 position. Thiophenoxy radical analogs of such phenoxy radicals are also contemplated. Typical stable nitroxy radicals are those having the general formula R1R2Nxe2x80x94O., where R1 and R2 are tertiary alkyl groups, or where R1 and R2 together with the N atom form a cyclic structure, preferably having tertiary branching at the positions alpha to the N atom. Examples of hindered nitroxy radicals include 2,2,5,5-tetraalkylpyrrolidinoxyl radicals, as well as those in which the 5-membered heterocycle ring is fused to an alicyclic or aromatic ring, hindered aliphatic dialkylaminoxyl and iminoxyl radicals such as (R3C)2Nxe2x80x94O. and R2Cxe2x95x90Nxe2x80x94O., diarylaminoxyl and aryl-alkylaminoxyl radicals such as the nitroxyl radical from alkyl diphenylamine, (Rxe2x80x94Ar)2Nxe2x80x94O., nitroxyl derivatives of dihydroquinoline light stabilizers and antiozonants (available from Ciba-Geigy), in monomeric and polymeric forms, and nitroxyl radicals derived from dibenzo-heterocycles such as phenothiazines and phenoxazines. A specific, preferred example is 2,2,6,6-tetramethyl-1-piperidinyloxy, which is available from Aldrich Chemical Company under the trade name TEMPO(trademark). This material is understood to be a representative of materials of the general structure 
where each R is independently alkyl or aryl, Rxe2x80x2 is hydrogen, alkyl, or aryl, X is hydrogen, alkyl, aryl, alkoxyl, carbalkoxy, carboxyalkyl, carboxamido- (xe2x80x94NHC(O)xe2x80x94 lower alkyl), or chloro, or where Rxe2x80x2 is absent and X is xe2x95x90O or xe2x95x90S. Esters and ethers thereof are also contemplated.
Hindered amine stabilizers are described in detail in Polymer Stabilization and Degradation, P. P. Klemchuk, Editor, American Chemical Society, Symposium Series 280, 1985, pages 55-97. These materials are closely related structurally to nitroxy radicals and can be converted thereinto by known means. Accordingly, the hindered amine structures illustrated in particular on pages 56, 58, 61, 91, 92, 94, 95, 97, and 97 of the above-cited document can be taken as illustrative of characteristic structures of a variety of stable nitroxy radicals.
The amount of stable free radical agent employed in the polymerization of the first block is typically 0.001 to 0.01 moles per mole of monomer, particularly for polymer molecular weights in the range of 10,000 to 100,000. Specific amounts can readily be determined and appropriately adjusted by the person skilled in the art.
Free Radical Initiators
Free radical initiators include peroxy compounds, peroxides, hydroperoxides, and azo compounds which decompose thermally to provide free radicals.
Free radical generating reagents are well know to those skilled in the art. Examples include benzoyl peroxide, t-butyl perbenzoate, t-butyl metachloroperbenzoate, t-butyl peroxide, sec-butylperoxydicarbonate, azobisisobutyronitrile, and the like. Numerous examples of free radical-generating reagents, also known as free-radical initiators, are mentioned in the above-referenced texts by Flory and by Bovey and Winslow. An extensive listing of free-radical initiators appears in J. Brandrup and E. H. Immergut, Editor, xe2x80x9cPolymer Handbookxe2x80x9d, 2nd edition, John Wiley and Sons, New York (1975), pages II-1 to II-40. Preferred free radical-generating reagents include t-butyl peroxide, t-butyl hydroperoxide, t-amyl peroxide, cumyl peroxide, t-butyl peroctoate, t-butyl-m-chloroperbenzoate and azobisisovaleronitrile.
The free radical initiators are generally used in an amount from 0.01 to about percent by weight based on the total weight of the reactants. Preferably, the initiators are used at about 0.05 to about 2 percent by weight. The molar ratio of free radical initiator to stable free radical agent is from about 0.2 to about 2:1, preferably from about 0.8:1 to about 1.2:1, even more often from about 1.1 to 1.2:1, frequently 0.8-0.9:1.
The reaction is usually conducted at temperatures ranging between about 80xc2x0 C. to about 200xc2x0 C., preferably between about 130xc2x0 C. to about 170xc2x0 C. Considerations for determining reaction temperatures include reactivity of the system and the half-life of the initiator at a particular temperature.
The choice of free radical generating reagent can be an important consideration. For example, when the reaction is conducted with a solvent such as a hydrocarbon oil, grafting of monomer onto the oil diluent may occur. It has been observed that the choice of initiator affects the extent of grafting of the monomer onto the oil diluent. Reducing the amount of monomer grafted onto the diluent usually results in an increased amount of monomer incorporated into the polymer block.
Peroxy- and azo-compounds are preferred.
Promoter
To further facilitate the polymerization, the polymerization can be conducted in the presence of a strong acid or an amine salt of an acid in an amount suitable to enhance the rate of polymerization, that is to say, a catalytic amount. Such an acid will normally have a pKa as measured in water of less than 4, preferably less than 2.5, and more preferably less than 2. A preferred amount of the acid or amine salt is an amount sufficient to reduce the pH of the reaction medium to 4 to 5. Otherwise stated, the ratio of an organic acid to the amount of the sterically hindered stable free radical is preferably about 1:1 to about 1:20, often to about 1:11 by weight. Either organic or inorganic acids can be used, for example mineral acids, sulfonic acids, acidic clays, organic sulfonic acids, carboxylic acids, acidic salts of any of these acids, and monoesters of sulfurous- and sulfuric acids. Preferred acids include carboxylic acids, sulfonic acids, phosphonic acids, and phosphoric acids. One such acid which has been successfully employed in the past is camphorsulfonic acid. See, for instance, U.S. Pat. No. 5,401,804. Other feasible acids include methane sulfonic acid, toluene sulfonic acid, sulfonic acid functionalized resins, 2-fluoro-1-methylpyridinium p-toluenesulfonate, trifluoromethanesulfonic acid, 3,5-di-t-butyl-4-hydroxybenzenesulfonic acid, and pyridinium p-toluenesulfonate.
The medium for polymerization of the blocks is not particularly critical and can be any such medium in which polymerization can be effected. Preferably, the medium is one in which the reactants are soluble, often a substantially inert normally liquid organic diluent. Examples include alkyl aromatics, preferably in relatively small amounts so that a relatively high concentration of monomer can be maintained. Solvents which readily transfer hydrogen atoms under radical conditions are preferably avoided. If such an alternative medium is used, it should also be one from which the initially formed block can be separated, such as by filtration, precipitation into a nonsolvent, or evaporation of the medium. Thus, the first block can be isolated prior to the further reaction to prepare the second block, while retaining the active polymerization site thereon. This retention of the active polymerization site is a characteristic and a benefit of the use of the stable free radical initiator. For best results in retaining the active polymerization site, processing of the polymer in the presence of hydrogen atom transfer agents, particularly at elevated temperatures, should be avoided.
Alternatively, polymerization can be conducted in the substantial absence of medium or solvent, that is, virtually neat. Trace amounts of materials which may be considered xe2x80x98diluentsxe2x80x99 as defined herein may be present. Trace amounts are essentially impurity amounts and are not amounts that have any significant effect on the process or the product.
Alternatively, the process to prepare subsequent blocks may be conducted without isolation of the preceding block.
The polymerization of monomers to prepare the second block can be accomplished either with or without employing additional free radical initiator and or promoter. Often, additional promoter or initiator is beneficial, and sometimes is necessary, to enable polymerization of the second block to proceed, especially at an acceptable rate.
In the process to prepare the A-B block copolymer, the weight ratio of vinyl aromatic monomer to acrylic monomer typically ranges from about 20:1 to about 1:20, preferably, from about 5:1 to about 1:10, most preferably from about 35:65 to about 65:35.
In the process of this invention, from about 5 to about 95 mole % of the charge comprising the at least one vinyl aromatic monomer, preferably, from about 50 to about 80 mole %, is polymerized to prepare the stabilized active polymer block (A). To the mixture of A-block polymer and unreacted vinyl aromatic monomer is then added the at least one acrylic monomer and optionally, additional vinyl aromatic monomer which is then further reacted to form the (vinyl aromatic-co-acrylate) (B) block. Optionally, additional free radical initiator and/or promoter may be utilized.
The polymerization process may be terminated by (d) reducing the temperature below the polymerization temperature of the monomers. The block copolymer may then be further worked up and isolated as a substantially solvent free dry polymer by stripping off diluent, if any, and volatile unreacted monomer, or by precipitation of the polymer from a solvent in which the polymer has limited solubility, and which solvent selectively takes up unreacted monomer.
Additional blocks may be incorporated into the polymer of this invention.
In one embodiment, the additional block is made up of the same vinyl aromatic monomers employed to generate the first block, block (A). The additional block is incorporated by (e) after step (c) adding and polymerizing, at an elevated temperature, at least one additional vinyl aromatic monomer wherein said additional vinyl aromatic monomer has the same composition as that charged to generate block (A). In this embodiment, the amount of monomers charged to generate the additional block ranges from about 0.2 to about 5 times that used to prepare the first (A) block. The additional monomer is charged and polymerized, optionally with additional free-radical initiator, in the same fashion as the preparation of the (B) block. The resulting polymer is an A-B-A triblock polymer.
In another embodiment, the additional block is made up of monomers selected from the group consisting of vinyl aromatic monomers, acrylic monomers, and mixtures thereof, wherein the composition of the third monomers is different from those employed to generate the (A) and (B) blocks. This additional block is incorporated by (f) after step (c) adding and polymerizing at an elevated temperature, at least one monomer selected from the group consisting of vinyl aromatic monomers, acrylic monomers, and mixtures thereof, wherein the composition of the third monomer is different from the monomers employed in steps (a)-(c). The additional monomers are charged and polymerized, optionally with additional free-radical initiator. The resulting polymer is an A-B-C triblock polymer. The weight ratio of the of monomers charged to prepare the additional block to the total weight of vinyl aromatic monomers charged to prepare the (A) and (B) blocks ranges from about 1:5 to about 10:1.
In a preferred embodiment, the vinyl aromatic monomer is selected from the group consisting of styrenes comprising at least one of styrene, an xcex1- lower alkyl substituted styrene, vinyl benzene sulfonic acid, and styrenes having C1-4 alkyl ring substituents, and the acrylic monomer is selected from the group consisting of acrylic acids, esters of acrylic acids, preferably those containing from 2 to about 50 carbon atoms in the ester group, acrylic amides, and acrylonitriles. Especially preferred is wherein the styrenes comprise styrene and the acrylic monomer comprises at least one methacrylic acid ester, especially an aliphatic ester containing from 9 to about 23 carbon atoms in the ester groups.
The process of this invention is conducted to provide copolymers having weight average molecular weights ({overscore (M)}w) ranging from about 1,000, more often from about 3,000, even more often from about 5,000 to about 500,000, often from about 10,000 to about 250,000, frequently up to about 25,000, frequently from about 3,000 to about 25,000, often up to about 15,000. In another embodiment, the resulting block copolymer has weight average molecular weight ranging from about 5,000 to about 250,000, often up to about 150,000, frequently up to about 100,000.
The molecular weight of the polymer is the total of the molecular weights of the individual blocks. In a preferred embodiment, the {overscore (M)}w of the A-block ranges from about 4,000 to about 80,000 and the {overscore (M)}w of the B-block ranges from about 4,000 to about 80,000 Preferred A:B weight ratios are 1:1 up to 2:1, preferably up to about 1.5:1. Molecular weights of the B-block and of third blocks are determined by subtracting the molecular weight of the A-block or for polymers containing more than two blocks, the total molecular weight of the previously prepared blocks, from the total molecular weight of the polymer.
As noted hereinabove, the block copolymers of this invention may comprise a third block. When the block copolymer is a triblock copolymer, the molecular weight of the third block typically ranges from about 4,000 to about 80,000.
Specific molecular weights of polymer are frequently dictated by the intended use. For the copolymers of this invention, when the polymer is intended to be used in gear lubricants, preferred weight average molecular weights ({overscore (M)}w) for each block range from about 5,000 to about 20,000, preferably up to about 12,000, with the preferred A-block to B-block {overscore (M)}w ratio of about 1-1.4:1. For use in hydraulic oils and in automatic transmission fluids, typical molecular weights range from about 10,000 to about 30,000, preferably up to about 20,000. For engine oils, for example for gasoline passenger car engines and for heavy duty diesel engines, the molecular weight for each block frequently ranges from about 40,000 to about 100,000, often up to about 80,000.
Molecular weights of the polymers are determined using well known methods described in the literature. Examples of procedures for determining the molecular weights ({overscore (M)}w and number average molecular weight, {overscore (M)}n) are gel permeation chromatography (GPC) (also known as size-exclusion chromatography), light scattering, and vapor phase osmometry (VPO). The GPC technique employs standard materials against which the samples are compared. For best results, standards that are chemically similar to those of the sample are used. For example, for polystyrene polymers, a polystyrene standard, preferably of similar molecular weight, is employed. When standards are dissimilar to the sample, generally relative molecular weights of related polymers can be determined. For example, using a polystyrene standard, relative, but not absolute, molecular weights of a series of polymethacrylates may be determined. These and other procedures are described in numerous publications including:
P. J. Flory, xe2x80x9cPrinciples of Polymer Chemistryxe2x80x9d, Cornell University Press (1953), Chapter VII, pp 266-316, and
xe2x80x9cMacromolecules, an Introduction to Polymer Sciencexe2x80x9d, F. A. Bovey and F. H. Winslow, Editors, Academic Press (1979), pp 296-312.
W. W. Yau, J. J. Kirkland and D. D. Bly, xe2x80x9cModem Size Exclusion Liquid Chromatographyxe2x80x9d, John Wiley and Sons, New York, 1979.
The following examples are intended to illustrate several compositions of this invention as well as means for preparing same. Parts in the following examples are, unless otherwise indicated, parts by weight. The amounts shown are sometimes expressly indicated as parts by weight (pbw) or parts by volume (pbv). The relationship between parts by weight and parts by volume is as grams to milliliters. Temperatures are in degrees Celsius (xc2x0 C.). Filtrations employ a diatomaceous earth filter aid. Molecular weight and polydispersity (PDI) values are determined using GPC. In several examples, the extent of conversion is determined during processing. Conversions are determined by taking an aliquot from the reaction mixture, precipitating polymer from the aliquot using methanol, and calculating the % of monomer converted to polymer. Molecular weight values for these in-process samples are obtained using GPC, with polystyrene standard, employing two 500 mmxc3x9710 mm columns in tandem, a Jordi-Gel Mixed Bed, Catalog # 15005, and a Jordi-Gel 500 xc3x85, provided by Jordi Associates, Bellingham Mass., USA. Values for the products of the examples are generated using GPC, with polystyrene standard, employing in tandem, four 300mmxc3x977.5 mm columns obtained from Polymer Laboratories Inc., Amherst, Mass. USA, consisting of three PLgel mixed bed C; 5 xcexcm, catalog #1110-6500 columns and one PLgel 100 xc3x85, catalog #1210-6120 column.